COASTAL CLASSIFICATION
There are two systems for classifying coasts:
1. The Geological Approach: Active Coasts and Passive Coasts
2. The Coastal Dynamics Approach: Primary and Secondary Coasts
In the first system, coasts are defined based on their position respective to plate
boundaries. Those coasts near plate boundaries that are moving, with the presence of
volcanic activity and earthquakes are considered “active” – and those located away from
these regions are considered “passive”.
In the second system, coasts are defined by the forces that shape them. Coasts formed by
non-marine geological forces are considered “primary” – and those formed by marine action
are considered “secondary”.
COASTAL DYNAMICS APPROACH:
SHEPARD COASTAL CLASSIFICATION SYSTEM
Primary Coasts
Secondary Coasts
•
Sinking Coasts
• Drowned River Valley
•
Wave-erosion Coasts
• Wave-cut beaches
•
Land-deposition Coasts
• Deltas
• Wind-deposition Coasts
•
Marine-deposition Coasts
• Barrier beaches, islands,
and spits
•
Volcanic Coasts
• Lava Flows
•
Bio-Shaped Marine Coasts
• Coral Reefs
•
Tectonic Coasts
• Fault-related Coasts
BEACH DYNAMICS
Beaches are dynamic.
What does this mean?
Dynamic can be “active”, “forceful”, and “changing”. Water motion is
constantly shaping and changing beaches. Without human intervention to
keep some coastlines intact, the appearance of a given beach can vary
greatly year-to-year.
Shape and Appearance of a Beach:
PARTS OF A BEACH:
The beach is the coastal area where loose
sediment has accumulated as land meets
the sea.
1.
2.
3.
4.
Off shore
Near shore
Foreshore
Back Shore
The position of these divisions of the beach
varies with the tidal and wave forces of the
area.
COASTAL DUNES
Sand dunes are formed by winds
blowing sand toward the land from
the dry part of the beach.
•
Well developed dunes:
typically have a primary dune at
the edge of the beach and
secondary dunes located farther
inland.
•
Vegetation - traps sand and
promotes dune growth and
stability.
Key Dune Formation Factors:




Sand is abundant
Strong and persistent on-shore winds
Large tidal range
Wide and gently sloped Beach
LONGSHORE DRIFT
•
Transport of sediment by a longshore
current (current that results from waves
approaching at an angle due to wind)
•
Moves sediment down the coast in the
direction of the wind
LARGE-SCALE SAND FEATURES
• Spits
• Bay-mouth Barriers
• Tombolo
• Barrier Islands
• Deltas
SPITS AND TOMBOLOS
•
Spit: area of accumulated sand that is attached to land at one end and
points in the direction of longshore drift
• Often have a hook shape
• Can continue to grow across the opening to a bay to form a bay-mouth
barrier
•
Tombolo: spits that extend between two islands, or from and island to the
mainland
• Decreases the effects of longshore drift because it slows the water down
and therefore the current can’t carry as much sand with it.
BARRIER ISLANDS
Barrier islands are islands composed of sediment that parallel the coast
and form where sand supply is abundant and a broad sea floor slopes
gently seaward.
•
Separated from the mainland by shallow bodies of water and are connected to
the ocean through tidal inlets.
•
Typical Barrier Island has 5 features:
•
•
•
•
•
•
Ocean Beach
Sand Dunes
Barrier Flat
Salt Marsh
Lagoon
Barrier islands are created via:



sand ridges isolated by rising sea level
Sand spits breached during a storm
vertical growth and emergence of longshore sand bars
BARRIER ISLAND FORMATION:
Two ways a barrier island can
form:
• Sea level rises to breach the
coastline, and fills in the
depression behind a ridge –
which then becomes an
island
• A longshore bar develops
and grows via sand
deposition to form an island
DELTAS
There must be the following conditions
for a delta to form:
• Large sediment load in the river
• Broad continental shelf region in the
ocean nearby
• Small tidal range
• Mild waves and currents
Why are there few deltas in the US?
• West Coast: Continental Shelf is too
narrow
• East Coast: Estuaries are common and
usually trap most river sediment
THREE BASIC DELTA TYPES:
River Dominated
•
•
•
•
Location: Area with a strong river, and mild ocean waves
River is primary shaping force
Characteristic Triangle Shape
Example: Mississippi River Delta
Tide Dominated
• Location: Area with strong tidal changes
• Tides redistribute sediment, and create tidal sand ridges
perpendicular to shore
• Characteristic ridges will form a tidal channel over time
• Example: Essex River Delta in Massachusetts
Wave Dominated
•
•
•
•
Location: Area with strong waves
Waves redistribute river sediment along beaches
Action forms dunes and spits
Example: Senegal River Delta in west Africa
CHAPTER 15 CLASSWORK QUESTIONS:
PART 1
For the following scenarios, determine whether the coastline would be considered primary or
secondary:
1. A volcanic island with coastlines of smooth, cooled lava flow
2. A tropic shoreline bordered by an immense coral reef
3. A coast that has been eroded away by intense wave action
4. A shoreline that occurs where a river meets the ocean
5. An ancient river valley that has been flooded over time by a rise in sea level
PART 2
6. How is longshore drift important to coastline shaping?
7. How do tides affect the divisions of a beach?
8. What are the differences between river-dominated, tide-dominated, and wave-dominated deltas?
9. Explain some types of large-scale sand features found along coasts.
10. Why would people want to modify coastlines?
HIGHLIGHTING COASTAL HABITATS AND HUMAN IMPACTS
PART 3
11. Explain the four types of estuaries.
12. How are estuaries important in the cycling of nutrients?
13. How do mangroves affect the coast?
14. What are the characteristics of salt marshes and lagoons?
15. Where are salt marshes found?
16. Describe how are marine organisms are able to build coasts.
17. What are the differences between fringing reefs, barrier reeds, and atolls?
18. Explain the differences between the following man-made coastal structures: groins, jetties,
breakwaters, and seawalls.
19. What problematic changes occur along the coastline due to human impacts?
20. Describe beach re-nourishment.
KNOWLEDGE CHECK:
Use the book and your notes to complete the questions on the following pages:
15-11, 15-20, and 15-26
Write the question out completely, and include just the answer below.
Oceanography April 28, 2014
Beaches
1. What are the factors that shape a beach’s appearance?
2. What does it mean to say a beach is “dynamic”?
3. List the parts of a beach in order moving from inland to the open ocean.
CHAPTER 15 PRACTICE EXTENDED RESPONSE QUESTIONS
1. Explain the difference between primary and secondary coasts and give an example of each.
2. How is a beach dynamic? What factors affect the dynamics of a beach?
3. Describe two ways a barrier island can form.
4. Characterize the roll that coral reefs can play in coastal shaping.
5. In what ways do humans impact coastlines. Provide at least two specific examples .